Hydrocarbon petroleum based lubricants are normally applied as a liquid or a viscous grease. However, in applications where the surface to be lubricated is part of a body rotating at a relatively high speed, conventional lubricants may be slung off into the environment or may creep onto an adjacent area where lubrication is neither needed nor desired. A problem such as this exists in the rail industry wherein there is a need for lubricating the flange on the periphery of railcar wheels to reduce friction and wear between the wheels and the sides of the steel rail on which the wheels run. Oil or grease applied to the wheel flanges is thrown off, polluting the area adjacent the track. In addition, a conventional lubricant quickly spreads from the flange onto the wheel tread and onto the crown of the rail, thereby reducing traction between the driving wheels of locomotives and the rail, and creating a potential safety hazard by increasing the distance needed to stop the train.
In attempting to avoid the above problems, solid lubricant sticks have been developed in the prior art, which may be used to apply a lubricating film to the flanges of railcar wheels. One of the commercially available lubricating sticks includes a catalytically cured molybdenum disulfide compound molded in a cylindrical foil wrapper. The lubricating stick is mounted in a tubular applicator and is biased against the flange of a railcar wheel by a weight.
A similar stick or rod-type lubricant comprises a graphite based lubricating composition core enclosed in a molded "electric furnace" graphite shell. The graphite stick is placed in a tubular applicator and is biased against the wheel flange with a helical coil spring.
The dry lubricant sticks of the prior art overcome some of the problems associated with lubricating railcar wheels using conventional oil or grease; however, they fail to provide a complete solution to the problem. Both types of prior art dry lubricant sticks are fragile, being made of hard, brittle materials, which tend to break easily. Each of the prior art dry lubricant sticks represents a maintenance problem because of their relatively small physical size and the rate at which they are applied. Due to their relatively short length, they must be replaced approximately every 4,000-6,000 miles--much too often to be practical for use on trains traveling several hundred thousand miles per year. In addition, it is impractical to mount a lubricant applicator on each wheel of the train, or even on each car. Ideally, one applicator should be mounted on each side of a train, e.g., on two opposite wheels of a locomotive. The applicator should apply a lubricant film to the wheel flange that is transferred to the side of the rail, and from the rail, to all the wheels of trailing cars, on that side of the train. The prior art solid lubricant sticks are unable to provide lubrication to more than a few wheels, because the dry lubricant provided in the sticks does not transfer well and does not attach or bond well to the metallic surface of railcar wheels that subsequently pass over the track.
Other solid lubricating compositions are known in the prior art that might be useful in this type of application. For example, in U.S. Pat. No. 3,729,415, a lubricating composition is disclosed comprising a hydrocarbon oil and polyethylene having an average molecular weight within the range of about 1.5 million to 5 million in proportions yielding a jelly-like gel. Related U.S. patents are U.S. Pat. Nos. 3,541,011 and 3,547,819, all of which teach that a compound of polyethylene and oil will have the physical characteristics of a liquid, a thin gel, or a rigid gel, depending upon the molecular weight and/or the amount used of the high molecular weight polyethylene.
A solid gel-type lubricant has a number of advantages over the lubricant sticks comprising graphite and molybdenum disulfide. The gel-type lubricant is not brittle and can easily be extruded or molded in almost any form. However, since oil is the lubricating medium in the solid gel, it is not retained on the track very well over an extended period of time and does not provide the long-term wear resistance or the ability to withstand extreme pressures characteristic of dry lubricants, such as graphite.
As an alternative to graphite, metallic powders are known to provide a substantial lubricating benefit when used as an additive in a petroleum based compound. For example, U.S. Pat. No. 2,543,741 teaches that a compound comprising flake copper, lead, and graphite in a petroleum based vehicle is useful for a thread sealing and lubricating composition. Also, in U.S. Pat. No. 4,204,968, a lubricant additive composition is disclosed comprising a lubricating liquid carrier containing a mixture of powdered copper and lead metal particles less than 20 microns in diameter which, it is suggested, function "as tiny ball bearings and platelets," operative to plate onto high wear areas.
Other additive materials are also known to enhance the load bearing capabilities of various lubricating base stocks. Zinc di(neo-alkyl) phosphorodithioate is such an additive and its use with cyclohexyl compounds is disclosed in U.S. Pat. No. 3,803,037. A lubricating additive is commercially available that includes synthetic sperm oil, zinc dithiophosphate, an organic molybdenum compound, lead naphthenate, and mineral oil, and it is intended to improve the wear resistance of liquid petroleum based oil to which it is added. However, the prior art has not taught the use of such additives in solid lubricants nor with dry powders, nor is it clear that a benefit would accrue from their use therewith, particularly, since the mechanism by which the additives function to improve wear resistance and to reduce friction is not clearly understood.
It will be apparent that the prior art does not include a lubricant composition that is entirely suitable and which meets all of the requirements for lubricating surfaces such as railcar wheel flanges. Accordingly, the present invention is directed to providing such a lubricant composition. Other objects and advantages of the present invention will be apparent from the description that follows hereinbelow.